1. Field of the Invention
The present invention relates to a memory device. In addition, the present invention relates to a semiconductor device on which a memory device is mounted. Further, the present invention relates to an electronic device on which a semiconductor device is mounted.
2. Description of the Related Art
In recent years, most various electronic devices such as computers can perform desired operations by using a variety of data. When the data is held in, for example, a memory device (also referred to as a memory) or the like, the data can be used temporarily or permanently. A memory device also refers to an external memory device (an auxiliary memory device) such as a hard disk or a flexible disk in a broad sense. However, a memory device almost always refers to a semiconductor memory device such as a CPU (central processing unit). Two main types of memory devices are a volatile memory and a nonvolatile memory. A volatile memory refers to a memory device in which data is lost even after the data is held. In addition, a nonvolatile memory refers to a memory device in which data can be held semi-permanently after the data is held.
Although a volatile memory has a possibility of losing data, it has an advantage of short access time. In addition, although a nonvolatile memory can hold data, it has a disadvantage of high power consumption. Memory devices each have features in this manner, and each of the memory devices is used in accordance with the kind or usage of data.
Among the memory devices, there is a memory device (hereinafter referred to as a resistive random access memory device) which changes the resistance of a memory element, determines voltage before change in the resistance and voltage after the change in the resistance, and holds the voltage as data. An example of such a resistive random access memory device is, for example, an organic memory, which is a kind of the nonvolatile memory. An example of such an organic memory is, for example, a memory (hereinafter referred to as a short-circuited type organic memory) which includes a memory element in which at least a single layer which contains an organic compound (hereinafter referred to as an organic compound layer) is provided between a pair of electrodes, decreases the resistance value of the memory element by applying high voltage between the electrodes to fluoride the organic compound layer so that the pair of electrodes are short-circuited, distinguishes a written state and an unwritten state from each other with the existence and nonexistence of the short-circuit, and holds voltage in each state (for example, Reference 1: Japanese Published Patent Application No. 2006-352104).